ocs_doc_api: Phase 2b-c (linear Dimension) — Phase 2 complete

- CreateDimensionLinear(DimensionSpec) op + GetDimensionMeasurement query (append-only).
- backend add_dimension_linear (Dimension::Linear via DimensionLinear::new) +
  dimension_measurement (linear/radius/diameter distance).
- Dimension bounds from measured + definition points; Dimension handle + measurement().
- spec Dimension family; api_reference + binding_schema regenerated; mocks + baseline.
- Test phase2c_dimension_linear_create_measurement_bounds -> 607 host lib + 8 crate
  + 3 consistency green. Phase 2 (full 2D + annotations) is now complete.

crates/ocs_doc_api/IMPLEMENTATION.md

@@ -68,7 +68,10 @@ Phase 2b (annotations/hatch/dimension typed ops), attributes + nested traversal
 - **Done (2b-b):** `Hatch` — `create_hatch(boundary, solid)` (`CreateHatch`,
   validates ≥3 points), `boundary()` → loops (`GetHatchBoundary`), bounds from
   boundary edges, delete. Covered by `phase2b_hatch_*` test.
-- **Remaining (2b-c):** `Dimension` (typed sub-types).
+- **Done (2b-c):** linear `Dimension` — `create_dimension_linear(first, second,
+  definition)` (`CreateDimensionLinear`), `measurement()` → distance
+  (`GetDimensionMeasurement`), bounds. Covered by `phase2c_*` test. Radius/diameter/
+  angular dimension sub-types are a later refinement.
 - **Unblocked:** `add_vertex` (polyline) and sweep profiles (Line/Circle/Arc/LwPolyline)
   are supported (Phase 0).